Can you view your email via web browser? This is also called webmail. Some popular email services, such as hotmail, Yahoo! Mail, and Google's Gmail are normally accessed via webmail. But, many email accounts provided by ISP's (Internet Service Providers) also allow accessing email both by email client such as Outlook Express or by logging on to your account via web browser interface.
My point is, if you can access your email account via web browser, you can see what's waiting to downloaded to Outlook Express before you download it and identify messages containing large attachments or have large files even though they have no attachment, and you can delete them before downloading messages to Outlook Express.